The traditional production methods for carbon black consist in a combustion of hydrocarbons by the supply of air. The quality achieved will be dependent on the supply of air or oxygen and the use of different amounts of oxygen in a surplus or a deficit. In the known methods substantial parts of the hydrocarbons are consumed in supplying sufficient energy for the decomposition, thus realizing a relatively low yield of carbon black. In addition to a low yield the combustion process will cause environmental pollution, since both carbon dioxides and nitrogen oxides will be produced. The waste gases from the processes will be able to be used only as fuel gas.
For the decomposition of hydrocarbons other pyrolytic methods have also been used in which plasma torches have been utilized, but it has not been possible to use these methods for continuous production due to deposits on the electrodes, which have led to stoppages in the process and expensive cleaning procedures.
Carbon which is formed by pyrolysis of hydrocarbons can be divided into two different qualities, viz. carbon black and coke (pyrolytic carbon). Carbon black is light and soft with low density and is produced in the gas phase, while coke is harder, has hign density and is produced on surfaces with relatively low temperatures, normally lower than 1100.degree. C.
From U.S. Pat. No. 4,101,639 is known a pyrolytic method for the production of carbon black where water vapour is injected into the plasma stream radially and tangentially with respect to the walls of the reaction chamber. The water vapour will avoid the formation of pyrolytic carbon and graphite in the carbon black.
The tangential stream of water vapour will protect the walls of the reaction chamber from high temperatures of the plasma stream and prevent deposition of condensed carbon on the walls. The water will however decompose and create oxygen containing groups on the carbon black surface and is this considered a disadvantage for most qualities of carbon black. Furthermore the water will decompose and create oxygen containing gases such as carbonoxides and nitrogenoxides which will pollute the off-gases in the process.
From DD 211 457 is known a method and an apparatus for the production of carbon black and hydrogen. A part of the hydrogen is recycled and is used as plasma gas. Feed stock in the form of hydrocarbons as liquid or gas is introduced radially via nozzles in one end of the reaction chamber and is mixed into a plasma stream at a temperature between 3500 K and 4000 K. The reaction chamber is equipped with tempering zones where the reaction products are quenched to a temperature of about 1100 K. The tempering zones in addition act as a heat exchanger and are used to preheat both the plasma gas and the feed stock. The disadvantage of the above method and apparatus is that the reaction chamber walls are cooled and thereby large temperature gradients arise in the reaction chamber in the area where the quenching of the feed stock occurs and uneven process condition and product qualities will be the result. In addition, deposition easily forms on cooled surfaces.